First off, how long has been over heating?
How long have you been chasing this problem?
What type of fan are you using?
Is the water pump correct for the direction of rotation?
Are the pulleys sized right where the water pump spins faster then the crankshaft?
Whats in front of the radiator?
What type of temp gauge are you using and have you verified it's accuracy?
What does the temp do at idle, low MPH, and HIGHWAY speeds?
More coolant doesn't effect the way it heats up or cools off, as long both radiator and engine are full with no air pockets, more coolant will not help or hurt. More coolant takes long to heat up and cool off, but it won't effect anything once the system is at operating temperature.
